sched/psi: Fix psi_seq initialization

JIRA: https://issues.redhat.com/browse/RHEL-110301

commit 99b773d
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Tue Jul 15 15:11:14 2025 -0400

    sched/psi: Fix psi_seq initialization

    With the seqcount moved out of the group into a global psi_seq,
    re-initializing the seqcount on group creation is causing seqcount
    corruption.

    Fixes: 570c8ef ("sched/psi: Optimize psi_group_change() cpu_clock() usage")
    Reported-by: Chris Mason <clm@meta.com>
    Suggested-by: Beata Michalska <beata.michalska@arm.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Phil Auld <pauld@redhat.com>

Author: auldp

kernel/sched/psi.c

@@ -176,7 +176,7 @@ struct psi_group psi_system = {
 	.pcpu = &system_group_pcpu,
 };
 
-static DEFINE_PER_CPU(seqcount_t, psi_seq);
+static DEFINE_PER_CPU(seqcount_t, psi_seq) = SEQCNT_ZERO(psi_seq);
 
 static inline void psi_write_begin(int cpu)
 {
@@ -204,11 +204,7 @@ static void poll_timer_fn(struct timer_list *t);
 
 static void group_init(struct psi_group *group)
 {
-	int cpu;
-
 	group->enabled = true;
-	for_each_possible_cpu(cpu)
-		seqcount_init(per_cpu_ptr(&psi_seq, cpu));
 	group->avg_last_update = sched_clock();
 	group->avg_next_update = group->avg_last_update + psi_period;
 	mutex_init(&group->avgs_lock);